This invention relates generally to the field of dielectric waveguide transmission line components operating in the millimeter wave frequency region, and more particularly, to a modulator or switch for controlling electromagnetic wave propagation in a dielectric waveguide circuit.
In millimeter-wave radar and communications systems where size, weight, efficiency and cost often dictate the use of the dielectric waveguide as the low-loss millimeter wave transmission line medium, switches are often required in order to modulate millimeter wave energy for systems applications or to isolate sensitive receiver components from damaging transmitter energy.
While the previous art in millimeter-wave switches is rather limited, earlier switch designs for use in metal waveguides operating in the millimeter wave region have centered around the use of a metal waveguide junction having a ferrite element to which an axial magnetic biasing field is applied to alter the effective permeability of the ferrite such that energy propagation in the guide is controlled. A device of this type is described by R. A. Stern in an article entitled "A Fast 3-mm Ferrite Switch," IEEE Transactions on Microwave Theory and Techniques, September, 1971.
In dielectric as opposed to metal waveguide structures, another type of switch is known. This configuration uses a dielectric transmission line having a semi-conducting epitaxial layer to which a bias voltage is applied. The change in the effective depletion depth of the epitaxial layer brought about by the bias voltage results in change boundary conditions along the waveguide wall thereby controlling wave propagation in the guide. This particular design requires that the operating frequency of the guide be located near the cut-off frequency which results in a device having a rather narrow frequency band of operation.
None of these earlier devices has been successful in providing a broadband ferrite waveguide switch having the capability of operating in the millimeter wave frequency region in a dielectric transmission line.